docs: def select_data(self, iteration_indices):
          """keep only data of `iteration_indices`"""
          dat = self
          iteridx = iteration_indices
          dat.f = dat.f[np.where([x in iteridx for x in dat.f[:, 0]])[0], :]
          dat.D = dat.D[np.where([x in iteridx for x in dat.D[:, 0]])[0], :]
          try:
              iteridx = list(iteridx)
              iteridx.append(iteridx[-1])  # last entry is artificial
          except:
              pass
          dat.std = dat.std[np.where([x in iteridx
                                      for x in dat.std[:, 0]])[0], :]
          dat.xmean = dat.xmean[np.where([x in iteridx
                                          for x in dat.xmean[:, 0]])[0], :]
          try:
              dat.xrecent = dat.x[np.where([x in iteridx for x in
                                            dat.xrecent[:, 0]])[0], :]
          except AttributeError:
              pass
          try:
              dat.corrspec = dat.x[np.where([x in iteridx for x in
                                             dat.corrspec[:, 0]])[0], :]
          except AttributeError:
              pass